Known as a conventional laser processing method in the above-mentioned technical field is one irradiating a planar object to be processed comprising an Si substrate with laser while locating a converging point within the object, so as to form a modified region to become a starting point region for cutting in the Si substrate along a line to cut the object (see, for example, Patent Literature 1).    Patent Literature 1: Japanese Patent Application Laid-Open No. 2004-343008